Calorespirometry responses of sugar-maple mature trees and seedlings to calcium and nitrogen additions in the Catskills Mountains, NY, USA

Background/Question/Methods

Sugar maple is an important component of the forests of northeastern North America and has been declining for several decades. Sugar maple decline may alter stand structure and long-term stability of its native habitat. The decline may be related to acidic-deposition induced changes in soil chemistry that alters availability of nutrients such as nitrogen (N) and calcium (Ca).  Gas exchange and metabolic activity are key eco-physiological processes that govern plant growth and health. Calorespirometry is a novel method of quantifying plant metabolic activities under optimum or stressful conditions. We quantified total metabolic rate (Rq), the rate of CO₂ production (RCO₂), and the efficiency of metabolism (CCe) in sugar-maple seedlings and mature trees in several sites (in the Catskills Mountains, NY) in response to a 2² factorial combinations of N and Ca soil additions during summers for two years. Calorimetric measurements were made using a Multi-Cell Differential Scanning Calorimeter. We also measured respiration rates (rate of CO₂production in the dark) using a LICOR-6400.

Results/Conclusions

Calcium addition had no effect on any of the responses measured. Nitrogen addition decreased (P < 0.03) both measures of respiration (CO₂ production) made by Clorespirometry and LICOR in mature trees only. However, the decrease did not coincide with any significant change in the efficiency of respiration. This is puzzling because increased rates of respiration is expected to show increased growth rates under optimum conditions and decreased growth rates (increased maintenance cost) under stressful conditions. But the efficiency of respiration should change accordingly, which was not observed in this study.  Contrary to our expectation, the correlation between measures of CO₂ production through Calorespirometry and LICOR was not significant for seedlings and was week (r = 0.5, P < 0.07) for mature trees.